A communication system for transmitting and receiving control information which is used for communication data transmission and processing is explained below.
A transmission node encodes communication data which is separated into a plurality of blocks having 8 bit length to a communication data code according to 8B/10B encoding rule and transmits the data. Details of 8B/10B encoding rules used here are disclosed in Japanese Unexamined Patent Application, First Publication No. Sho 59-10056. Control information transmission processing is performed for each control information which is separated into M parts (M is an integer) of blocks having 8 bit length during a period in which communication data code is not transmitted in which each block is encoded to control information 10B code according to 8B/10B encoding rule and is transmitted.
A transmission node decodes the communication data code which is received thereat according to 8B/10B encoding rules and obtains communication data which is separated into a plurality of blocks having 8-bit length. Also, the transmission node restores the control information by performing the control information transmission processing in which M parts of control information 10B code are decoded according to 8B/10B encoding rules.
In the communication system which is realized using the above-mentioned conventional technology, when a bit error occurs in the control information 10B code which is being transmitted, a control information which is received at a receiving node has a different value from a value in the control information which is transmitted from the transmission node. Such a difference may cause a control error and may be a cause of a serious problem. The 8B/10B encoding rule has an error detecting device such as running disparity in which a different code is used according to a difference (running disparity value) between total number of “1” (one) which are coded and total number of “0” (zero) which are coded. However, it is not possible all the time to identify the code in which an error occurs by running a disparity detecting method; therefore, it is difficult to determine whether or not a control information code contains an error.
Also, when a repeater which generates an 8B/10B code exists on a transmission line, a running disparity is normalized in the repeater; therefore, only an error of disparity which occurs between a repeater and a receiving node can be detected. Therefore, error detecting capacity is insufficient. Furthermore, when there is a transmission interval in which data transmission is performed in a different encoding format from the 8B/10B encoding rules in the transmission line, the running disparity detecting method cannot detect an error occurring at such an interval.
The present invention was made to solve the above-mentioned problems. An object of the present invention is to provide an encoding method for control information in a communication system for separating all of the control information or a portion of control information into M (M is an integer) parts of control information blocks having N (N is an integer from 1 to 7) bit length, adding a control information parity having a predetermined (8−N) bit length to each of the control information blocks i (i is an integer from 1 to M), encoding the control information blocks i into M parts of control information code having 8 bit length according to a predetermined control information bit array, performing a control information transmission processing. In an encoding method according to the present invention, the control information parity and the control information bit array are determined such that the Hamming distance of each of the control information code is at least d (d is an integer from 2 to 8), and the Hamming distance of each of the control information 10B code is at least D (D is an integer from 2 to 10). By doing this, it is possible to detect control information in which an error occurs during data transmission and to correct it.
Also, another object of the present invention is to provide an encoding method for control information in a communication system in which the control information code which is obtained by performing the control information receiving processing is separated into the control information block and the control information parity at the receiving node, and the parity check is performed to the control information block and the control information parity, and an error processing is executed when an error is detected. Thus, the control information in which an error occurs during the data transmission is detected and corrected.